
a class of objects \(X,Y,Z,...\) ,

a category of morphisms \({B}(X,Y)\)  for every pair of objects \(X,Y\) , where the unit object in \({B}(X,X)\)  is denoted \(U_X\) , and

natural isomorphisms \(a\) , \(r\)  and \(l\)  that witness associativity, right unitality, and left unitality, respectively and that satisfy certain axioms that the reader can find, for example, in [1]}, [2]}.

